The present invention relates to a polypropylene resin composition and more particularly to a polypropylene resin composition which is composed mainly of a crystalline ethylene-propylene copolymer, has excellent moldability and can provide a molded article of good balance particularly in rigidity and impact resistance, good mechanical properties and excellent appearance Said polypropylene resin composition can be utilized in large-sized parts for automobiles, particularly instrument panels for automobiles.
Crystalline polypropylene is in use in various molded articles in which physical properties such as rigidity, resistance to heat deformation and the like are required. However, having insufficient low temperature properties and being a non-polar highly-crystalline polymer, crystalline polypropylene has poor impact resistance and poor coatability and cannot be used in applications in which rigidity, resistance to heat deformation, impact resistance and coatability are required together
In order to improve the impact resistance and coatability of crystalline polypropylene, there have been proposed, for example, a polypropylene composition which is a blend of a crystalline ethylene-propylene block copolymer as a crystalline polypropylene with an amorphous ethylene-propylene copolymer, and a polypropylene composition which is a blend of crystalline ethylene-propylene block copolymer, an amorphous ethylene-propylene copolymer and various polyethylenes.
In these polypropylene compositions, however, the rigidity, resistance to heat deformation, and the like inherently possessed by crystalline ethylene-propylene block copolymers are reduced.
In order to improve the drawbacks of the above polypropylene compositions, Japanese Patent Application Kokai (Laid-Open) No.53-64257 describes an invention titled "Impact-resistant Resin Composition". The document discloses a resin composition with improved low temperature impact resistance, comprising a crystalline ethylene-propylene block copolymer, an amorphous ethylene-.alpha.-olefin copolymer and talc. The document describes that the resin composition, as compared with conventional crystalline ethylene-propylene block copolymers, is substantially improved in low temperature impact resistance, rigidity and coatability, and provides Examples for supporting the description. The above composition, however, is insufficient in rigidity-impact resistance, balance and appearance. Consequently, the molded article obtained from the composition is unsuitable for use in applications such as parts for automobiles, particularly instrument panels where mechanical properties and appearance are required, although the article can find limited applications where appearance is negligible.
There have also been disclosed various polypropylene compositions comprising, as a filler other than talc, a granular filler (e.g. calcium carbonate) or a fibrous filler (e.g. glass fiber). However, in the polypropylene compositions comprising a granular filler, the molded articles have in sufficient rigidity; and in the polypropylene compositions comprising a fibrous filler, although the rigidity is improved significantly, the impact resistance is low and the molded articles have poor surface appearance and give rise to warpage and, deformation. For example, Japanese Patent Application Kokai (Laid-Open) No. 62-91545 proposes a polyolefin resin composition comprising a polyolefin, a thermoplastic elastomer, a fibrous reinforcing agent, talc and calcium carbonate. This composition, however, tends to yield poor appearance (e.g. silver streaking) during injection molding and has a small improvement in rigidity because it contains calcium carbonate. Japanese Patent Application Kokai (Laid-Open) No. 61-69848 proposes a polypropylene resin composition comprising a polypropylene resin, a fibrous filler, talc and an elastomer. This composition, however, causes deformation when molded into large-sized parts for automobiles because it contains a large amount of a fibrous filler.
Japanese Patent Application No. 62-324396 proposes a polypropylene resin composition comprising a crystalline ethylene-propylene block copolymer, an amorphous ethylene-propylene copolymer, talc and fibrous magnesium oxysulfate. The composition has insufficient rigidity and is improper for use in large-sized parts for automobiles.
The technique of compounding an olefinic resin and a hydrogenated block copolymer as used in the present invention to obtain a composition was already proposed in, for example, Japanese Patent Application Kokai (Laid-Open) Nos. 58-206644, 58-215446, 59-223745, 60-166339, 61-28547, 61-28548, 61-34047 and 61-34048. All of the compositions proposed in these documents contain large amounts of a hydrogenated block copolymer and a softening agent and consequently have low rigidity. In these compositions, even if the amount of the hydrogenated block copolymer is reduced to increase the rigidity, the tensile elongation is decreased.
Japanese Patent Application Kokai (Laid-Open) No. 57-51735 proposes a composition comprising a crystalline ethylene-propylene block copolymer, a hydrogenated block copolymer and an amorphous ethylene-propylene copolymer as used in the present invention. This composition, however, contains no inorganic filler and has low resistance to heat deformation and low rigidity. Therefore, the composition cannot achieve the object of the present invention.
Thus, the hitherto known polypropylene resin compositions mentioned above have been unable to provide a molded article having good balance in rigidity and impact strength, good mechanical properties, excellent appearance and good moldability and have found no use in, for example, large-sized parts for automobiles, particularly instrument panels.